With T5, even 20x should be within the range of possibility as determined by the average raven apperance rate estimate of ~27.5%, and t5 was possible without orbs even with my old raven estimate of 25%, and I’ve done it before personally. T5 should be possibly with a 3 bounty troop team containing a legendary captain, but its a little tighter on sigils (avg mod needed 20-21x). An average of 26x is needed if we use the 27.5% model for a t4 purchase, you’d may or may not fall just short if you don’t orb anything but still have a perfect run with a full bounty team.
T3 was still impossible with any mathematical model I applied for fixed raven appearance rate and orbing the bounty captain up to mythic (avg needed 34x mod even with a ~27.5%-27.78% estimated raven appearance rate). You need a bare minimum of 52 plays, so 21 starting sigils is a few starting sigils short of the most generous fixed rate estimate. I was working on a variable rate model (starting at 30% appearance rate, tapering off to 25% or possibly less) that is a bit more complicated, but I haven’t gotten around to gathering all the data for it yet. My current rough estimate even under that model, starting at 30% appearance rate with a decently slow decay rate is that t3 would fall just short.
By the way, you need a bare minimum of 55 total plays (2100 * 28 + 35 * 200 * 28) to accumulate the total 250,000 points needed with a 28x multiplier. A 27.78% average raven rate estimation with a starting sigils of 24 (day 1 t4 purcahse) would put you at at average of 54 overall plays +/- (or possibly just + or not +) one raven, meaning the above sample (t5 purchase, perfect run, finished with 1 sigil left on day 1 so 24 starting sigils with 1 remaining, total of 55 plays) is within this fixed-rate model.