What you've said doesn't make any sense.
Ignite between 5.0 and 5.1 has not changed. You will still get the same Ignites you are getting now. You will build them in the same way, you will proc Pyros using Heating Up the same way. The only thing that the Combustion tooltip change suggests is changing is that Combustion will tick for almost 2x as much damage as it currently does (almost, because the Pyro dot is removed, but that was an almost irrelevant part of the damage anyway).