i am definitely no expert on reactions because i don’t use them on my site. but i suspect you might be able to edit and override some of the properties of the discourse-reactions-picker with CSS:
.discourse-reactions-picker {
position: absolute;
inset: auto auto 0px 0px;
margin: 0px;
transform: translate(172px, -28px);
width: [insert width here];
height: [insert height here];
}