Hi Ross!
Well I have good news and bad news for you..... the good news is, you are doing everything just perfect, Amesiella monticola is one of three plants that are really prone to aborting spikes (Aerangis elisii and Aerangis brachycarpa to some degree thereafter). I have tried absolutely everything to stop it from happening and the only thing that seemed to work for me was move fans in front of the plants when in bloom and the abortion rate dropped by 45%. I wish I could say I figured that out but someone else told me to try that and when I asked why I was told to just do it!
Interestingly enough though, I tagged the aborters on the second year, and they continued to abort every year thereafter. Not once did I have to tag a bloomer as an aborter, so I suspect it is something genetic, but thats far beyond my expertise. The air movement does help though.