UBIQUITI Bullet M2 16dBm maximum transmit power

UBIQUITI Bullet M2 have 28dBm (630 mW) transmitter. But OpenWrt allow only 16 dBm maximum when set 28dBm for example:
Current power: 16 dBm + 12 dB offset = 28 dBm
Why?

iw list | grep -A 15 Frequencies:
Frequencies:
* 2412 MHz [1] (16.0 dBm)
* 2417 MHz [2] (16.0 dBm)
* 2422 MHz [3] (16.0 dBm)
* 2427 MHz [4] (16.0 dBm)
* 2432 MHz [5] (16.0 dBm)
* 2437 MHz [6] (16.0 dBm)
* 2442 MHz [7] (16.0 dBm)
* 2447 MHz [8] (16.0 dBm)
* 2452 MHz [9] (16.0 dBm)
* 2457 MHz [10] (16.0 dBm)
* 2462 MHz [11] (16.0 dBm)
* 2467 MHz [12] (disabled)
* 2472 MHz [13] (disabled)
* 2484 MHz [14] (disabled)
valid interface combinations:

iw reg get
global
country US: DFS-FCC
(2400 - 2472 @ 40), (N/A, 30), (N/A)
(5150 - 5250 @ 80), (N/A, 23), (N/A), AUTO-BW
(5250 - 5350 @ 80), (N/A, 23), (0 ms), DFS, AUTO-BW
(5470 - 5730 @ 160), (N/A, 23), (0 ms), DFS
(5730 - 5850 @ 80), (N/A, 30), (N/A), AUTO-BW
(5850 - 5895 @ 40), (N/A, 27), (N/A), NO-OUTDOOR, AUTO-BW, PASSIVE-SCAN
(57240 - 71000 @ 2160), (N/A, 40), (N/A)

phy#0
country US: DFS-FCC
(2400 - 2472 @ 40), (N/A, 30), (N/A)
(5150 - 5250 @ 80), (N/A, 23), (N/A), AUTO-BW
(5250 - 5350 @ 80), (N/A, 23), (0 ms), DFS, AUTO-BW
(5470 - 5730 @ 160), (N/A, 23), (0 ms), DFS
(5730 - 5850 @ 80), (N/A, 30), (N/A), AUTO-BW
(5850 - 5895 @ 40), (N/A, 27), (N/A), NO-OUTDOOR, AUTO-BW, PASSIVE-SCAN
(57240 - 71000 @ 2160), (N/A, 40), (N/A)

iwinfo wlan0 tx
12 dBm ( 15 mW)
13 dBm ( 19 mW)
14 dBm ( 25 mW)
15 dBm ( 31 mW)
16 dBm ( 39 mW)
17 dBm ( 50 mW)
18 dBm ( 63 mW)
19 dBm ( 79 mW)
20 dBm ( 100 mW)
21 dBm ( 125 mW)
22 dBm ( 158 mW)
23 dBm ( 199 mW)
24 dBm ( 251 mW)
25 dBm ( 316 mW)
26 dBm ( 398 mW)
27 dBm ( 501 mW)
** 28 dBm ( 630 mW)