Electronic ballast ratings
Every ballast is different.  There is no pattern or rule.  Sometimes the sales literature doesn't even agree with the data sheet - I've had to send ballasts back for that reason.  

The data sheet (which is not the sales pamphlet or sometimes even the instruction sheet in the box) will list every supported bulb size, usually with wiring diagrams for each different configuration. 

I don't see a data sheet for this ballast.  This is as close as Google gets me. 

They also seem to make a ballast for a single 18 watt bulb, here.  That's a bad sign.  Distributors don't like carrying a huge variety of ballasts, so manufacturers try to make ballasts work on as many configurations as possible.  The fact that they make a 1-18W ballast as well as a 1-36W, certainly suggests one can't do both jobs.