Variable scope in SASS each loop - sass

Question

I am trying to generate css class names using an #each loop in SASS and I am facing some confusion regarding the scope of a variable declared within the loop.
The variable $infix is meant to prefix the generated class name with a unique break-point-name ('sm','md','lg'...etc), only if the $break-point-width is not = 0
The problem is, the value of the $infix variable, ie, the break-point-name, is the same on each iteration of the loop, although I expected it would be unique per each iteration.
SCSS
$config: (
phone: (
break-point-width:0px,
break-point-name: xs
),
tablet: (
break-point-width:600px,
break-point-name: sm
),
laptop: (
break-point-width:900px,
break-point-name: md
),
desktop: (
break-point-width:1200px,
break-point-name:lg
),
);
#each $key, $map in $config {
$break-point-width: map_get($map, break-point-width);
$break-point-name: map_get($map, break-point-name);
$infix: if($break-point-width == 0px, null, -$break-point-name);
#media (min-width: $break-point-width) {
#for $i from 1 through 2 {
.foo#{$infix}-#{$i} {
content: 'bar';
}
}
}
}
Compiled CSS
#media (min-width: 0px) {
.foo-1 {
content: 'bar'; }
.foo-2 {
content: 'bar'; } }
#media (min-width: 600px) {
.foo-sm-1 {
content: 'bar'; }
.foo-sm-2 {
content: 'bar'; } }
#media (min-width: 900px) {
.foo-sm-1 {
content: 'bar'; }
.foo-sm-2 {
content: 'bar'; } }
#media (min-width: 1200px) {
.foo-sm-1 {
content: 'bar'; }
.foo-sm-2 {
content: 'bar'; } }
As seen in the compiled css output, the first iteration of the loop does not prefix the class name with the value of the $infix variable as was expected. In the remaining iterations all class names are prefixed with the 'sm' break-point-name. This is confusing, as it is seen the value of the $break-point-width variable is unique in each iteration, shown in the generated #media queries, but the value of the $break-point-name variable is the same in each iteration.
I am assuming the $infix variable, hence its value, is not scoped to each iteration of the loop and is only declared once.
I would really appreciate if someone could help me understand the cause of this behavior and how I could solve this problem.
With much thanks and appreciation,