DSCP / ToS in UDP Profile not working

There is another option to set DSCP, that is in pool parameter :

By setting Pool Advanced Parameter, ToS to Server, we are able to mark the outgoing packet :

[root@bigip:Active:Standalone] tmp  tmsh list ltm pool /NWP/dns_pool
ltm pool /NWP/dns_pool {
    ip-tos-to-server 42
    members {
        /NWP/server1:domain {
            address 172.16.20.1
        }
    }
    partition NWP
}

Using the parameter, I can apply DSCP to the outgoing packet.

09:08:00.312106 IP 172.16.1.33.51840 > 172.16.20.1.53: 44978+ A? f5trn.lab. (27) out slot1/tmm1 lis=/NWP/vs_dns
    0x0000:  452a 0037 ed5e 4000 ff11 20ea ac10 0121  E*.7.^@........!
    0x0010:  ac10 1401 ca80 0035 0023 6d77 afb2 0100  .......5.mw....
    0x0020:  0001 0000 0000 0000 0566 3574 726e 036c  .........f5trn.l
    0x0030:  6162 0000 0100 0101 1001 0000 010b 2f4e  ab............/N
    0x0040:  5750 2f76 735f 646e 73                   WP/vs_dns
09:08:00.317369 IP 172.16.20.1.53 > 172.16.1.33.51840: 44978 NXDomain 0/1/0 (68) in slot1/tmm1 lis=/NWP/vs_dns
    0x0000:  4500 0060 2c00 0000 4011 e14a ac10 1401  E..`,...@..J....
    0x0010:  ac10 0121 0035 ca80 004c 2624 afb2 8183  ...!.5...L&$....
    0x0020:  0001 0000 0001 0000 0566 3574 726e 036c  .........f5trn.l
    0x0030:  6162 0000 0100 01c0 1200 0600 0100 0029  ab.............)
    0x0040:  ec00 1dc0 1204 726f 6f74 c012 0000 0006  ......root......
    0x0050:  0001 5180 0000 0e10 0024 ea00 0009 3a80  ..Q......$....:.
    0x0060:  0110 0101 0001 0b2f 4e57 502f 7673 5f64  ......./NWP/vs_d
    0x0070:  6e73                                     ns

Still it did not answer the question about why protocol profile does not have any effect to the VS.