AXI narrow transfers

I would appreciate assistance on the following:

Suppose a bus master with 128bit data width.

This master access a 64bit slave via AXI matrix as follows:

awaddr = 0x4000_909F

awsize = 0x0 (8bit write)

awlen  = 0x0 (single trans)

wstrb   = 0x0080;

wdata  = 0xABCDEF01_10FEDCBA_12345678_87654321 (I've marked in red the relevant byte according to wstrb value)

1. Is this a valid transaction from a 128bit master to a 64bit slave?

    (note that addr 0x4000_909F aims at the byte MSB of the data ; 0xAB in my example)

2. What would you expect the wstrb value on the 64bit slave.

I get wstrb = 0x00

Thank you in advanced.