If your plane as a big roll rate advantage and high drag in a turn, such as a 190, the flat scissors is a good and under-rated defensive move. Try to start it early to show your intentions at a flat scissors, as this move is best if they try to counter it.
At about d800 I'll start with small quick cuts to bleed E and prevent the snipers from getting a good shot. I'll stay full throttle through this part as I need to keep a little E to burn for a high AoT when things get closer. These scissors are only maybe 1.5 seconds a side. Your opponent is probably keeping his E to close in through these early parts, since 190s are usually so fast they don't usually want to cut throttle until they are well into range for thier guns solution.
When they start getting to d400 that's when the real fun of the flat scissors starts. I have three goals here. First and foremost is bullet dodging. Even in a flat scissors I don't keep entierly flat. Try to judge where your opponents nose is on each pass and pull away from it. If he's a little nose high I'll keep myself a few degrees below the horizon to get under his guns. If he's in a bit of a dive I'll try to get a little above him.
There are two basic situations at this point depending on the style of my opponent. Either he's flying straight and only banking a little while dumping as much E as he can to stay back, or he's trying to scissor with me. The good ones let me do all the work and aim for the crossing shots while flying reasonably straight. They will still bank their wings toward me in case I try to break out, but they arn't turning, just bleeding E with flaps, gear, and anything else they can find.
The bad ones keep rolling toward me and trying to turnfight my scissors. The reason this is bad is that my supperior rolling plane is spending much longer in the actual turns then their plane, so I'm going to get more control over their E state. Because they are turning they arn't going to cut throttle as well as the waiters (takes E to turn, so turnfighters keep the engine going), so I get to control their E state by determining when they turn and when they fly level. The more I cross em the more they are in level flight, keep it up and I'll get the overshoot and scissor behind em pretty quick.
Beating the good ones requires that I watch for one of two vulnerabilities in their fight. If I can get them to stay low on a pass where I go extra high, creating some verticle seperation as well as getting them a little faster then me, I can probably cut throttle and pull right down into em for the reverse. This is the basic verticle seperation reversal. If they don't give me seperation I'll have to press for a pure overshoot. All I can say about doing this is I transpose into a rolling scissors when they get very close and I look for them to get get too far ahead to cleanly pull up onto my six, then I cut throttle. There are many types of rolling scissors, but the only ones 190s are good for are the locked ones. If they give me AoT for a stalling roll I'll stay on the bottom and start to run. If they are in a flapper I can probably get enough E to achieve seperation for a new reversal merge. If they get flaps up really fast I just transpose back into a flat scissors.
There's one more outside chance counter to watch for, but I didn't mention it earlier as it's not specifically related to the flat scissors. Many people will try for high barrel rolls or yo-yos to stay behind without shedding all their E. Oddly enough while the high yo-yo is a counter to an early flat turn, a flat turn or low yo-yo (depending on your E state) are the counters to an early high yo-yo. I just turn clean and pull verticle when they start getting over the top. The closer to nose to nose I can get from the flat turn the more effective the counter. When I'm either most of the way around on them or when they are topping out and getting ready to dive back at me I pull up and either shoot up past their nose if they are nose up or pull up under them if they are nose down. This works like a stallfighter technique. I pull up to start my stall later then theirs, while they are forced nose down because they bled all their juice in the pre-mature verticle move. As long as I clear their lfr I get a stalling snapshot on the overshoot no matter what they do. One successful reversal is all I need, so that's as far as I'll take the high yo-yo scenario.
Anyway, I hope you can visualize this enough to start playing with the flat scissors. It's a fun game that pretty much nobody plays anymore.
-p.