Bitumen backed tiles are very stiff and usually have a grey or black backing, you can test one by lifting it and rubbing the edge against a hard surface, it will leave an oily black/brown line.
I would not recommend using solvents or gels on them unless you are going to extract off almost immediately.
Its true that gels sit on top but get any near a join and up will pop the oil with a nice brown stain.
A company we know cleaned 3500 sq ft of carpet tiles in West London and used various solvents in the process and extracted after wards, all looked lovely.............Until the next day.
Great swathes of brown staining all over the floor, it was not restorable and cost their insurance £25k to get it replaced.
We do not recommend HWE on carpet tiles, we bonnet clean them all with good results, as mentioned they must be pre-vacuumed otherwise soil wick back will occur.