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.
K