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()))
    s=set(a)
    if(len(s)==1):
        print("-1")
    else: 
        mx=max(a)
        res=0
        for i in range(0,n):
            can=False
            if(a[i]==mx and i-1>=0 and a[i-1]<a[i]):
                can=True
            if(a[i]==mx and i+1<n and a[i+1]<a[i]):
                can=True
            if(can):
                res=i+1
                break
        print(res)