Maybe the real life effective angle was 40 degrees with that type of ASDIC. But it could have been that the uboat would still hear some of it above that. Just not enough to reflect a solid detectable ping back to the escort. Every microphone or speaker has a certain fall-off directional emission pattern. The edges of the cone are usually defined where the intensity is halved (-3 dB) with reference to the maximum level. So with enough amplification it might still be heard outside of the angle.
Also, with hindsight as they didn't know this yet at the time, if the sun has warmed up the upper layer of water the sound rays keep curving back to the surface and bounce down shallow again. Creating what is known as a surface layer. That would make the escort been heard by the uboat at longer distances than the escort would be able to effectively detect it.
But I doubt this is modelled to real life in the game at the moment. Devs have made it clear that the finer touches on the game will be made later.
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