I use my Google voice number as my main number at my desk. The calls ring in Gmail and I answer them there as well as make calls there from my address book. With fellow Gmail/GApps users, I also receive calls via the "voice chat" feature in GMail. However, ever since I got my Galaxy S3, if I am not active in the GMail window, voice chats ring only on my phone and Google Voice calls do not ring at all unless I go back and do something in the GMail window prior to the call. The calls just ring and ring and eventually go to voicemail (in the case of Google Voice calls). Google voice is configured to send calls only to my PC - I do not want to receive calls on my Android while I am at my desk.
This Chrome extension offers an always-running background process for Google Chat. This has worked for Google Voice for me and may give the GV/gmail chat protocol the priority that you seek (If you happen to be using Chrome). Ideally the fix should come from Google making GV a higher priority, but this could be a good work-around for you.