I think his question is how to get nearer once get in the position showed in his picture, rather than how to make an initial approach.
I don't know how sensitive escorts in SH4 but in plain SH3, they're not too good, so you could just dive slightly deeper than periscope depth and be quiet and wait until escorts past you and then you get in the middle of convoy. And this can be done in the middle of day.
With hardcore mod it's no longer possible, so attacks are basically limited in night time only (except you have long range torps and risks for a long range shot). In night time, according to reality, you should be able to get quite near even on the surface (no moon light and of course you have to slow down to make less noise and wake etc).
Books etc says to set yourslef up on about 45 degrees from convoy's course to approach. Yeah, then, I have not read any book what exactly to do after. Of course it depends on situation but at any rate, what they tell you is that you somehow time the escorts movement and sneak into them undetected
So, after all, I'm also not answering the question

But the thing is, real captains in the era had much much less information than us and thay couldn't
practice or
experiment with real enemy. So maybe it's really up to you, building your own best method..