It should be a higher power of YOUR understanding. Don't worry about what others in the meeting's HP is.
I think it might be worth broaching this in a meeting (maybe in the coffee break) to someone you feel is reasonable - I'm fairly sure you'll be pleasantly relieved by the responses. Getting a sponsor so you can discuss this stuff before embarking on Step 4 would also be a good idea. Step 4 and 5 without a sponsor while you're already feeling a bit wobbly re the whole HP issue sounds like a bit of a risk to me.
I suppose I'm lucky because in the meetings I go to, people have very varying ideas of what their HP is, and organised religion features very little in it.
There are some great threads on the 12-step sub-forum that might be helpful where others have has similar worries that might be worth looking at...
Step 2 - SoberRecovery : Alcoholism Drug Addiction Help and Information http://www.soberrecovery.com/forums/...on-aa-god.html