Tips on Evading Detection Before Attack?

[Raskol]

I've got TMO 2.0 installed with the easier AI optional mod, playing RSRDC.

It's Jan 1942, my second patrol, I'm ranging around in the makassar strait in a Sargo class, no damage. Clear skies, a light breeze, calm seas. I pick up a big convoy with over a dozen smoke trails on the horizon, and maneuver to a spot about 5nm in front of them, directly in their path, go under. From the sonar station I can hear about 4 destroyer escorts in front of the convoy, so I turn my nose directly into them and head down to 450 feet at 1 knot on silent running---the idea being, I guess, to keep moving into the middle of the convoy, wait until the forward escorts have passed, then pop up in there and pop off some shots at point blank range. I know I'll be detected once I get shallow, but I don't care by that point---I'm shooting then going back under. Evading after the fact isn't the problem, I just want to get in there.

The problem is, it seems that no matter what I do, the escorts detect me as soon as they're close. The thermal layer is at 150 feet. I'm sitting at 450 feet, giving them the slimmest possible profile, but I'm still getting pinged as soon as they pass over me. Then it's alarm sirens and the whole convoy is zig zagging before I even start my ascent.

So is this sort of approach doomed to fail? Or just how deep would I have to go in order to avoid getting pinged?

Also, I've been operating under the assumption that the active sonar cone is directional--iow, if I start going up to periscope depth once I'm in the rear hemisphere of the escorts, I won't be pinged. Is that correct, or does it extend all the way around, so that the only real blind spot is underneath the escort?