Defining your rating system as 1-4 and then using ".5" a bunch is just extra confusion. It also deviates from everything else being a whole number (and requires more than just a glance, as the 5 stands out more than the decimal). Could simply readjust it/define your ratings differently. A bit like the difference between S tier and SS tier or something.
At the very least, an added description for the .5 that you use would help. "Carry anybody comfortably/with room for error" or something to that effect? Whereas T1 implies a need for pretty solid play?