UDSelect width changes markedly depending on context

Hi Everyone, hoping someone can tell me where I’m going wrong here…

I have a simple udselect component - if I put that directly under the new-udpage - fine.
As soon as I put it inside any other component, with udselect width drops to a fraction of the screen (enough to wrap text in the select items). For example, my first attempt was a udrow with 3 equal columns ( size 4), with a udcard in the first column, and udselect in that.

The select took up only half the card? I expected it to stretch to close to 100% of the card.

Examples (multiple versions) are:
    New-UDPage -Name "OrganisationalGroups" -Content {
    
    New-UDSelect -Label "I'm Full Page width" -Option {
        
        $Cache:OrgGroups['SAN'].keys | Sort-Object | ForEach-Object {
            Write-UDLog $Cache:OrgGroups['SAN'][$_] -Level info
            New-UDSelectOption -Name $Cache:OrgGroups['SAN'][$_].name -Value $Cache:OrgGroups['SAN'][$_].samaccountName
        }
    }

    New-udlayout -Columns 3 -Content {
      
        New-UDSelect -Label "I'm half a column wide" -Option {
            
            $Cache:OrgGroups['SAN'].keys | Sort-Object | ForEach-Object {
                Write-UDLog $Cache:OrgGroups['SAN'][$_] -Level info
                New-UDSelectOption -Name $Cache:OrgGroups['SAN'][$_].name -Value $Cache:OrgGroups['SAN'][$_].samaccountName
            }
        }
    }

    new-udrow -Columns {
        New-UDColumn -size 12 -Content {
            new-udcard -Size large -Content {
                New-UDSelect -Label "I'm fraction a card wide" -Option {
                    
                    $Cache:OrgGroups['SAN'].keys | Sort-Object | ForEach-Object {
                        Write-UDLog $Cache:OrgGroups['SAN'][$_] -Level info
                        New-UDSelectOption -Name $Cache:OrgGroups['SAN'][$_].name -Value $Cache:OrgGroups['SAN'][$_].samaccountName
                    }
                }
            }
        }
    }
  }

I presume I’m doing something wrong?