1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

for _ in range(int(input())):
    n=int(input())
    a=list(map(int,input().split()))
    max1=max(a)
    i=0
    j=1
    found=0
    while j<n:
        if a[i]==a[j]:
            i=i+1
            j=j+1
        else:
            found=1
            break
    if found==0:
        print(-1)
    else:
        for i in range(n):
            if i==0:
                if a[i]==max1 and (a[i+1]!=max1):
                    print(i+1)
                    break
            elif i==n-1:
                if a[i]==max1 and (a[i-1]!=max1):
                    print(i+1)
                    break
            else:    
                if a[i]==max1 and (a[i-1]!=max1 or a[i+1]!=max1):
                    print(i+1)
                    break
            