With your hearing loss it would be hard to obtain benefits without earmolds with appropriate small vents.
It should be measured by e.g. ruler, but 3P seems too long and hearing aids may hanging very loosely on your ears. It’s worth to try e.g. 0P or 1P (numbers are for length, from 0 to 4; P is for Power receiver).
See here:
I am not sure if you could obtain better benefits from UP receivers, but it can only be determined by REM. For example 0UP receiver or 1UP receiver.