Seeing balls after reflow is not because of excess initial particle size, but due to process error like expired or poorly mixed paste, temperature profile problem etc. Such balls are usually much larger than the initial particles and result in from the solder not flowing properly to the pads and component legs. When everything works as it should, the flux in the paste pulls all the solder into the pads. In addition to flux quality (age/mixing) problem, other causes can be too large paste openings, too much paste (it has to go somewhere!), or general messy application - if you get paste where it doesn't belong, it melts into balls.
Grade 3 should really be small enough for your purposes, just don't use grade 2. Only if you do some very fine 0.3 or 0.4 mm pitch parts you need to use grade 4. You may still want to try changing solder paste brands to see if that helps, so you may want to give grade 4 paste a try. Getting reflow process work reliably is combination of sometimes nearly blind experimentation (where luck is an element, sadly) and more rigorous process control.