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

from sys import stdin,stdout
for _ in range(int(stdin.readline())):
    n=int(stdin.readline())
    a=list(map(int,stdin.readline().split()))
    if len(set(a))==1:
        print(-1)
        continue
    mx=max(a);p=0
    for i in range(n):
        if i==0 and a[i]==mx:
            if a[i]>a[i+1]:
                p=i
                break
        elif i==n-1 and a[i]==mx:
            if a[i]>a[i-1]:
                p=i
                break
        else:
            if a[i]==mx:
                if a[i]>a[i+1] or a[i]>a[i-1]:
                    p=i
                    break
    print(p+1)