Ok, so here's how the multiplier works
Doflamingo states that Luffy is using the tensile force to raise his power several times above it's limits
For a long time, I've been very wrong about how this actually works. I always saw it with the simplicity as "Well Gear 4th: Boundman is 3-4x stronger than his previous limit of power", but that is very very wrong. What Doffy is referring to is that the COMPRESSION effect of Luffy's Gear 4th attacks, basically when he compresses his fist into itself, that's what specifically increases Luffy's power by several times. This means that the compression effect of Boundman doesn't multiply the power of Gear 2nd or Gear 3rd attacks. What it means is that it is increasing Luffy's basic Gear 4th Punches and Attacks by several times.
So we have a non-compressed Gear 4th punches and attacks, where Luffy can punch and kick without compressing his fist, and it's only when he compresses his fist, that it's power is multiplied by several times. That means every time that Luffy compresses his fist like he does in Gear 4th, he is multiplying his punches power by several times. This would be a univeral multiplier.
Now luckily for us, Luffy basically always compresses his fist and uses these attacks for scaling, so that doesn't change much in itself. But we do have one big huge factor. LUFFY USES BASIC GEAR 4TH FLEXING AND ARM MOVEMENTS TO BREAK 9 OF DOFFY'S STRINGS
This means that non-compressed basic Gear 4th punches and attacks scale to 9 Doffy Strings and would therefore scale to 1.1 Gigatons (
Large Mountain level). Now when Luffy compresses his fist and releases attacks like Kong Gun, Rhino Schneider, Culverin, Leo Bazooka. etc. Luffy is multiplying his power by several times beyond that basic non-compressed Gear 4th attacks that can casually break 9 of Doffy Strings. This would mean Gear 4th Boundman's AP scales to 3.3 to 4.4 Gigatons (
Large Mountain level+ to
Island level).
This also majorly helps solidify the gap between Gear 4th Luffy and Ulti. Luffy was gonna use basic non-compressed Gear 4th attacks to break out of Ulti's grasp and therefore would only need the non-compressed strength against Ulti, likely meaning any compressed Gear 4th attack would have clapped Ulti's cheeks.
Now as we obviously know, Hao Infusion Base Luffy's attacks clashed evenly with Hybrid Kaidou's Hao Infusion and he obviously can use Gear 2nd and Gear 3rd to hurt Kaidou with this power as well.
But then he also stacks Gear 4th's compression effect on top of these effects with Over Kong Gun. This would make Over Kong Gun at bare minimun 3-4x stronger than the Base Hao Infusion attacks.
Now when Luffy clashes his Bajrang Gun with Kaidou's Blazing Bagua, throughout the entire clash, Luffy's fist has still not unleashed the compression effect.
And it's only in the final blow that Luffy releases the compression effect and ultimately defeats Kaidou
This means the Bajrang Gun would also be 3-4x stronger than his regular Gear 5th attacks
So yeah, that was my essay and realization of everything