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(input())):
    n=int(input())
    a=list(map(int,stdin.readline().split()))
    ma=max(a)
    if len(set(a))==1:
        print(-1)
        continue
    for i in range(n):
        if i==0:
            if a[i]==ma and a[i+1]<a[i]:
                print(1)
                break
        elif i==n-1:
            if a[i]==ma and a[i-1]<a[i]:
                print(n)
                break
        elif a[i]==ma and (a[i+1]<a[i] or a[i]>a[i-1]):
            print(i+1)
            break