Hmm. Something seems a little out of wack, as XP doubles every 2 levels, but you're scaling things linearly here. One Level 1 creature is worth 40 XP to a combat vs a group of 4 Level 1 PCs, so things work out here. But a Level 2 creature is worth 60 XP, not 80, and 60 * 4 = 240, not 320.

If you're indexing the creature XP to Level 1, the XP curve looks like this (where Approx XP uses a 240 baseline for Level 2 as they do in the books, and XP is using exact scaling):

Level	XP	Approx XP	Linear Scaling
1	160.0	160	160
2	226.3	240	320
3	320.0	320	480
4	452.5	480	640
5	640.0	640	800
6	905.1	960	960
7	1280.0	1280	1120
8	1810.2	1920	1280
9	2560.0	2560	1440
10	3620.4	3840	1600
11	5120.0	5120	1760
12	7240.8	7680	1920
13	10240.0	10240	2080
14	14481.5	15360	2240
15	20480.0	20480	2400
16	28963.1	30720	2560
17	40960.0	40960	2720
18	57926.2	61440	2880
19	81920.0	81920	3040
20	115852.4	122880	3200
21	163840.0	163840	3360
22	231704.8	245760	3520
23	327680.0	327680	3680
24	463409.5	491520	3840
25	655360.0	655360	4000
26	926819.0	983040	4160
27	1310720.0	1310720	4320
28	1853638.0	1966080	4480
29	2621440.0	2621440	4640
30	3707276.0	3932160	4800

Using Level 1 indexed XP (let's call it XP_1, for the sake of brevity), your example above becomes 560 XP shared between either 4 equally levelled characters (140 XP) or 3 unequally levelled ones, with it being unclear how exactly to divvy up the reward.

I'm not convinced your use of level as weight works, due to the fact that level power does not scale linearly. Instead, I would look to the players' contribution to the party's XP pool. PCs have an encounter XP budget that's the same as monsters', by level, which means the mixed party has 160+240+240 = 640 XP between them. The Level 1 character contributes 160/640 = 0.25, or 1/4 of the party's XP, so they should probably receive 1/4 of the XP reward.

560 * 0.25 = 140 XP, which is what they would get if it was a party of 4 Level 1 PCs.

The other two characters each contribute 37.5% of the party's XP, so they would each receive 560 * 0.375 = 210 XP, which would scale to 150 XP in the standard rolling XP window.

I've been kicking this math around for a while now on scrap paper. There's been a small spike in questions around XP and balance over on r/Pathfinder2e, though, so maybe I'll work through his a little and make it a little more accessible/searchable.