Increasing fax rate. T38FaxMaxDatagram issue

Hello,

I’m trying to increase fax sending speed from 14400 to 33600 on asterisk 13.9.1.
I’ve enabled t38 passthrough on our asterisk and on speed 14400 faxing works grate, but when I’m trying speed 33600 fax-data didn’t transferred and I get these messages in console

`[May 20 14:46:28] WARNING[3134][C-00000006]: udptl.c:1162 ast_udptl_write: UDPTL (SIP/2007-0000000d): UDPTL asked to send 98 bytes of IFP when far end only prepared to accept 93 bytes; data loss will occur.You may need to override the T38FaxMaxDatagram value for this endpoint in the channel driver configuration.
[May 20 14:46:28] WARNING[3134][C-00000006]: udptl.c:1162 ast_udptl_write: UDPTL (SIP/2007-0000000d): UDPTL asked to send 175 bytes of IFP when far end only prepared to accept 93 bytes; data loss will occur.You may need to override the T38FaxMaxDatagram value for this endpoint in the channel driver configuration.`

I’ve tried to set different values(90, 93, 100,400) for T38FaxMaxDatagram param in sip.conf and udptl.conf but it doesn’t help. And in invite always the same:
a=T38FaxMaxDatagram:397

Any help would be much appreciated.
Thank you in advance.

For chan_sip
http://wiki.kolmisoft.com/index.php/How_to_change_T38FaxMaxDatagram
For chan_pjsip
edit pjsip.conf
add t38_udptl_maxdatagram=1400