Having Front Height and Rear or Middle Overhead would be fine, but if you can do ceiling speakers, I'd strongly suggest doing front/rear overhead and removing your front height.Have a question on what speakers to add to my 9.1 In-ceiling speakers and where to put them behind or in front listening area, or RH? I have 9.1 with FH and want to go to 11.2. Also would it sound funny if I have 2 as FH and add 2 in-ceiling.
When looking at any upgrade you need to keep in mind where you want to be in the future and plan for that final configuration.
Atmos speakers can be:
Whatever your current configuration, the end goal is this:
Any step you take, make sure the end result is on that graphic.
Dolby 7.1.6 Speaker Guide