You may indeed be able to get a larger vent with a BTE. Particularly if rather than being super small your ear canal is just very oval/narrow. An earmold is also easier to modify, so if the first fit is occluding you can shorten the vent bit by bit to see if you can get to a good balance of feedback management versus occlusion.
Keep in mind that even at the low frequencies, you don’t have “normal” hearing. You have mild hearing loss. If the problem you are running into is that you feel your ears are plugged up, that you aren’t hearing low frequencies as well as you should, that is not occlusion that we worry about–that can be replaced by cranking up the gain on the hearing aids (and closing the vent). Troublesome occlusion comes as an unpleasantly weird effect on your own voice, even when the hearing aids are in and off. It also comes as uncomfortably loud body noises, such as crunching. Some people with your loss aren’t actually that sensitive to it, and some people are very sensitive to it–it depends on your individual anatomy (and to some degree, your tolerance for things sounding different).
Given your loss, I wouldn’t expect the high frequencies to be impacted negatively with a move to a standard tube BTE. If you stay with a RIC, what is going to work best will again depend on your anatomy. Sometimes a shallow, wide-open skeleton will be better than a dome for feedback, but sometimes a smaller dome will be better if it can be seated more deeply. I would recommend you go with what you are the most comfortable with and work within those parameters to optimize the fit. Some people are more comfortable in BTEs (I have a mild BTE bias because of their robustness and fit) but some people are more comfortable in RICs (i.e. if they are sensitive to BTEs making their ears feel hot or to the weight of the device).
It you’re looking to do some trial and error, there will likely be a non-refundable expense associated with the earmolds. Good quality earmolds are more expensive than they seem like they should be–I run into a lot of sticker shock for earmolds in particular, but our margins there are actually very low.