Based on my initial audiogram (green line) my HCP ordered custom earmolds with vents.
Based on the green line Genie 2 recommends having a 1,0mm vent:
However, during the initial fitting, she did an in-situ measurement since I noticed the audiogram is significantly different from what I usually have. This resulted in the pink line.
Based on the pink line Genie 2 recommends having a 1,4mm vent:
Is it troublesome that my vent is too small? Does this has any disadvantages?
I wouldn’t say so your hearings worse than mine and I have 1.4mm vents.
How does it sound to you? If your voice sounds reasonable, it should be fine. My take is venting is very much a “in the ballpark” kind of thing, not something precise.
I’m not sure. The only downside of smaller vents is any possible occlusion effects I’d guess. Upside would be fewer feedback issues. Am I missing out any other possible effects?
That’s basically it, but remember it’s easy to prevent feedback if you lower the gain. Smaller vents lets you get more gain without feedback.
The gain, vent size and feedback are a balancing act the fitter deals with. Once the correct hearing aids are selected for your hearing loss this balancing act begins.
Ah, good to know things can be very simple sometimes 
Did your HCP do the in-situ audiometry before or after REM? If before REM, then did he/she have Genie 2 represcribe the gain curve to the new in-situ result before doing REM? If your HCP did REM before doing the in-situ audiometry and have Genie 2 re-prescribe the gain curves to the new in-situ result and didn’t do REM again afterward, then all the REM adjustment done prior to the in-situ audiometry will have been lost due to the re-prescription.
That would be a more important question to ask than the vent size being a little bit smaller than the recommended default based on the in-situ result. When/if you gain curves are chosen to be re-prescribed based on the new in-situ result (instead of basing on your original audiogram), as long as you leave your vent selection to its actual size of 1.0mm, then Genie 2 will use this information to re-prescribed properly to this 1.0mm size for you.
The only time you may want to change to the recommended 1.4mm vent is if and only if you feel like the 1.0mm vent size you currently have is too occlusive and you prefer to go bigger to the 1.4mm size and actually take action to do so. Then you need to update that info in Genie 2 and re-prescribe the gain curves based on that new size, then your HCP should rerun REM for you because your fitting has now changed.
Exactly what I thought! Thank you.
She did REM after the in-situ as one should.