Most ignitions manufacturers advise against using a single battery for ignition AND receiver. They also advise against regulators.
Many ignitions will work well on one, or two LiPo cells, depending on ignition design.
In my tow plane I have:
3S LiPo for boxer ignition
5S2P Sanyo Eneloop on Emotec for receiver safety
5S Eneloop for on board tow line winch
1x Eneloop for Venom temp gauge