BIG-IP DNS Topology LB selection - topology score vs QoS score

Im trying to figure out when/why topology score vs qos score is being used for the DNS LB.

When we use topo LB in WIP to select a certain pool I get the following:

SIN-F5I01 from {my internal src IP} [test.glb.lab.int A] 

[topology selected pool (AMS-Exchange-GTM_Pool) - topology score (10) is higher] 

[topology skipped pool (FRA-Exchange-GTM_Pool) - topology score (0) is not higher] 

[topology selected pool (AMS-Exchange-GTM_Pool) with the highest topology score (10)]

When I do the same on a pool to select a certain pool member:

SIN-F5I01 from {my internal src IP} [time.glb.lab.int A] [pool member check succeeded (chi-ntp01.labint)  

[QoS selected pool member (chi-ntp01.lab.int) - QoS score (0) is higher] 

[pool member check succeeded (sin-ntp01.lab.int) [QoS selected pool member (sin-ntp01.lab.int) - QoS score (429496729600) is higher] 

[pool member check succeeded (ams-ntp01.lab.int) - [QoS skipped pool member (ams-ntp01.lab.int) - QoS score is not higher] 

[QoS selected pool member (sin-ntp01.lab.int)]

In both cases we are using Topo LB and dont assign any gtm-score to any VIP.

Question:

Is this just the default behavior - pool member selection vs pool selection?

On the QoS score, how exactly is this calculated? I figured changing the weight in the topo record changes the score (weight 1 = QoS score (42949672900), weight 10 = QoS score (429496729600))

Many thanks in advance