If you're defending a strat and you didn't see a dot slowly ooze toward your strat from an enemy rear field, then you should assume it is low.
It takes closer to an hour to climb an super heavily loaded buff to 30,000 feet and it moves forward below 200mph.
If a strat suddenly comes under attack without the raging clue of a dar bar moving toward it over the course of an hour, then you should perform your intercept in the belief that they are low.
This is best done upping a fast and heavily armed fighter and flying it NOE to the strat.
If you generate a dar bar on the way, they will surely bail before you get there.
What you accomplish is often landing hits before they know you are there......if you fly low enough to obscure your icon.
If they bail then, you still get the kills and they are just as dead.
If it turns out they are at 30k, even a LA7 can climb up to 30k.......as long as your NOE trip out to the strat is done at reduced power in the interest of fuel economy.
I've hit bombers at 30k with an I16.........just haven't gotten a good intercept run on a B29 yet in the I16.
You can "catch B29s" that are above 25k feet even with a 110g if you know how to psych the b29 driver into descending for more speed simply by staying relatively close.
I often find them missing control surfaces when I catch up if they don't bail because of the damage/fear.