I assume you have EAN 28 as back gas because you are looking to dive down to the limit of rec diving which is 130 ft. If you normally use EAN 28 as backgas, then have your pony filled with EAN 28 as well and there will be no need for gas switching on your computer. If you normally use air, then EAN 28 will keep you the the plus side if you ever have to switch to your pony. If you normally use EAn 32, the difference will be minimal. BTW, what backgas do you normally use???
In my book, there is a difference between equipment malfunction and emergency and both could force you to switch to your pony. In some situation, handling badly a simple malfunction could result in the end state of a dive emergency.