Just to go back a touch,
i get asked about this stuff so its more to help folk that are starting out welding but when spotting/puddlewelding heres what may make life easier.
i will assume the metal on the underside is clean ,if your using weldthru then please leave it to fully cure
next,hole size, there is a point at which the hole is so smallm that you will not get sufficient heat into the base part quick enough and a puddle will form that may look like a weld but is onlly adhering to the sides of the ypper part(the hole)
with the right nozzle and amperage etc i will go down to 5mm as a minimum but prefere7-8mm.
next you need to ensure stuff is clamped

on the gutter runs for instance, i clamp 4 times to do 4 tacks and hold the item in the correct place then inbetween them again and again so im spreading the heat out along the length (10' will expand and cause a curve which is in this case what i wanted)

the weld on the left is acceptable, the aim here is to get full penetration into the lower metal which is 14g and as the pool is expanding you allow it to encroach on the edge of the upper piece and so weld to it stopping when it is flush,anymore means work with a disc (x 100's of spots !)
the weld on the right is too full

also invest in a tin of tipdip it will help keep the biz end happier
mm